A routine evening hop from Newark to New Orleans turned into an in-flight security incident on Monday night, when a passenger on United Airlines flight UA2174 reportedly tried to force his way into the cockpit while claiming he had a bomb in his backpack.

The aircraft, a Boeing 737 MAX 9 registered N17422, left Newark Liberty International at 9:26 PM — two minutes ahead of schedule — and was on descent through 20,000 feet when the pilots set the transponder to squawk 7500, the universal code for hijacking or unlawful interference. That silent alert tells air traffic control something is wrong without tipping off whoever is causing the problem. Flightradar24 data shows the jet still touched down at Louis Armstrong New Orleans International at 11:07 PM, a full 52 minutes early, so the incident did not delay the flight.

Details are still thin, but the crew's handling of the situation was textbook. As well as the squawk code, the pilots sent an ACARS data message to other United aircraft describing an 'attempted level four' — the most severe threat category, meaning an attempted or actual cockpit breach. The passenger, described as a man in dark clothing with a backpack, had reportedly been moved to the rear of the plane and seated with cabin crew by the time it reached the gate, where police were presumably waiting.

It is the second hijack scare on a United flight in a matter of weeks. In October, a 737 MAX 8 flying from Las Vegas to Newark diverted back to Harry Reid International after a flight attendant spotted a passenger texting about hijacking the plane. That passenger, a 25-year-old man who had been drinking, was arrested on landing for making false terrorism threats.

For travellers, the takeaway is reassuring rather than alarming. Squawk 7500 — seen most famously this year during an attempted hijacking of a flydubai flight from Dubai to Tel Aviv — exists precisely so crews can flag trouble quietly and instantly. Cockpit doors are reinforced, crews are drilled for exactly this scenario, and in both recent United cases the flights landed safely and the individuals involved were taken into custody. If you ever notice a sudden return to the departure airport or an unexpected priority descent, there is a chance a code like 7500 or the general emergency 7700 is behind it — and it usually means the system is working.

For frequent flyers on the busy Newark-New Orleans corridor, Monday's events are worth knowing about but are no reason to change plans. Report anything suspicious to crew, keep your seatbelt fastened, and trust that the pilots have far more tools at their disposal than most passengers realise.

Story first reported by Simple Flying.